A suspected chemical incident that led to the evacuation of London City Airport may have been caused by a passenger accidentally discharging CS gas before check-in, police have said.
A canister, believed to be "a CS gas or spray", was discovered by police during a search on Friday afternoon.
About 500 people were evacuated from the east London airport at 16:00 BST after some passengers felt unwell.
Two people were taken to hospital and 26 others treated at the scene.
A spokesperson said that while "the cause of the incident has not yet been confirmed, officers are investigating if it was the result of an accidental discharge".
"At this early stage officers are investigating whether it may have been discarded by a passenger prior to check-in," the spokesperson said.
The Met have said they are not treating the case as terrorist-related.
David Morris, 28, had been checking in for a BA flight to Edinburgh when he "started to cough to the point I was not able to keep talking".
"It was getting quite bad and we saw other people starting to cough at the same time. The people behind the desk were coughing the most and quite aggressively," he said.
Chris Daly, 35, from Southend, told the BBC he had just landed on a flight from Glasgow when he heard the fire alarms.
"When we got into the airport terminal building we could hear the fire alarms going on, then there were announcements in three different languages saying this is a fire alarm and the crew were directing us at the baggage carousel to evacuate the building," he said.
London Fire Brigade said sweeps of the airport were carried out by crews wearing protective equipment.
"No elevated readings were found and the building was ventilated, searched and declared safe," a spokesperson said.
The airport was reopened after about three hours and is running as normal.